Project Summary/Abstract Many survivors of premature birth and perinatal brain injury suffer from long-term neurological sequelae. These newborns urgently need early effective and safe interventions for neuroprotection. Our group is interested in the pharmacology of a voltage-gated potassium channel called Kv1.3 (KCNA3), which plays an important role in immune cell activation by modulating membrane potential to influence intracellular mechanisms such as Ca2+ signaling. Our group previously found that Kv1.3 is required for the pro-inflammatory state of microglia, and has provided evidence to support Kv1.3 as a therapeutic target for Alzheimer's disease and adult stroke. Recently we extended our study to a mouse model of neonatal lipopolysaccharides- sensitized hypoxic-ischemic brain injury (LPS-HI), in which activation of mononuclear phagocytes (MPs, which include microglia, monocytes, and macrophages) plays a key pathological role. This model replicates a major form of perinatal brain injury in which perinatal infection/inflammation sensitizes the brain to subsequent HI insult and augments brain injury. We showed that Kv1.3 knockout or selective pharmacological inhibition of Kv1.3 mitigates the LPS-HI brain injury. Surprisingly, while Kv1.3 RNA and protein levels were increased in MPs isolated from LPS-HI brains, whole-cell patch-clamp failed to detect significant plasma membrane Kv1.3 (PM-Kv1.3) channel activity on the MP cell surface. A logical inference is that an intracellular pool of Kv1.3, such as Kv1.3 in mitochondria, described in some tumor cell lines, is activated instead. Indeed, our recent data show increased mitochondrial Kv1.3 (mito-Kv1.3) in MPs isolated from LPS-HI brains. This discovery marks an important difference in MP activation mechanisms between the neonatal LPS-HI model and the adult models of stroke, Alzheimer's, and LPS injection, as in the latter the PM-Kv1.3 activity is significantly upregulated. Our hypothesis, therefore, is that pro-inflammatory activation of MPs, critical for neurotoxic actions in LPS-HI, requires Kv1.3, with a major contribution from mito-Kv1.3. To test this hypothesis, we will address three Aims. In Aim 1 we will use a targeted deletion approach to distinguish the respective contributions of Kv1.3 in residential microglia and Kv1.3 in invading monocytes. Such a determination will help understand dynamic neuroimmune mechanisms involving monocyte-microglia interactions and neuronal injury, about which little is known in neonatal brains. In view of our novel findings regarding mito-Kv1.3, in Aim 2 we will validate mito- Kv1.3 as a potential therapeutic target for LPS-HI brain injury. Pharmacological tools that are able to selectively target PM-Kv1.3 and mito-Kv1.3 will be tested for their efficacy in mitigating brain injury in the LPS- HI model. In Aim 3, we will further test the hypothesis that mito-Kv1.3, via regulating mitochondrial membrane potential, facilitates reprogramming of mitochondrial metabolic state to drive functional polarization. Our goal is to uncover the mechanistic link between mito-Kv1.3 and MP activation state, and design promising new therapeutic approaches to mitigate perinatal brain injury.